1. Field of the Invention
The present invention relates to a method of forming an insulating film such that the insulating film made of an organic material is stacked on a silicon oxide film.
Description of Related Art
2. Prior Art
Hitherto, a film made of an organic material has been employed in a process for manufacturing a semiconductor apparatus to serve as a resist mask for patterning a predetermined film or injecting ions into the same.
In recent years, reduction of the dielectric constant of an interlayer insulating film has been required in order to reduce the capacity of wiring, which has been enlarged because the semiconductor devices have been fined. As a film which is capable of realizing a low dielectric constant, which cannot be realized by inorganic film, an organic film has attracted attention.
As compared with the SiO.sub.2 film having a relative dielectric constant of 3.9 and the SiOF film having a relative dielectric constant of 3.7 to 3.2 each of which has been employed as the interlayer insulating film, the polyimide resin film and the fluorine resin film have considerably low relative dielectric constants of 3.5 to 3.0 and 2.5 to 1.9, respectively. Therefore, use of an interlayer insulating film made of an organic film in a semiconductor device having a design rule of 0.18 .mu.m or smaller has been considered.
When the organic film is employed as the resist mask, long-term reliability has not been required for the adhesive property with respect to the film serving as the base because the organic film has been removed before the semiconductor device is manufactured. However, the organic film is retained after the semiconductor device has been manufactured in a case where the organic film is employed as the interlayer insulating film. Therefore, the organic film needs to stably adhere to the base film for a long time. The reason for this is that insufficient adhesive property between the organic film and the base film tends to causes a defect in the semiconductor device. In a case where an insulating film made of fluororesin is formed on a silicon oxide film, the adhesive property between the two films deteriorates. If the base silicon oxide film has slight irregularity, the concave portions cannot sufficiently be plugged with the insulating film made of the fluororesin.
FIG. 1 shows wafer having such a structure that a second silicon oxide film 104, an organic insulating film 105 made of fluororesin and a third silicon oxide film 106 are stacked to form an interlayer insulating film for covering a wiring pattern 103 formed on a first silicon oxide film 102 on a silicon substrate 101. To form the organic insulating film 105 made of fluororesin, a process is performed in which the second silicon oxide film 104 is formed, coating formed such that the fluororesin is dissolved in a solvent is applied and the solvent is removed by heat treatment in a temperature range higher than a glass-transition level. However, the formed organic insulating film 105 has voids 107 formed in the wiring pattern 103. The reason for this is that the fluororesin having a considerably high coefficient of thermal expansion at temperatures higher than the glass-transition level, involves great volume change when the heat treatment is performed for removing the solvent.